A flat disk or "wafer" of single crystal silicon is the basic substrate material in the semiconductor industry for the manufacture of integrated circuits. Semiconductor wafers are typically created by growing an elongated cylinder or boule of single crystal silicon and then slicing individual wafers from the cylinder. During the process of building and connecting the integrated circuits on the wafer, the wafer must be transported from processing station to processing station as well as transported within the same processing station many times. The devices that hold the wafers are generally referred to as wafer chucks. Common examples are wafer carriers (shown in FIG. 2) and robotic end effectors (shown in FIG. 3) that are commonly used in chemical-mechanical polishing machines as shown in U.S. Pat. No. 5,498,199.
Vacuum systems that are coupled to wafer chucks are well known in the art to assist in the transportation of the wafers. Common pressures within these vacuum systems are between -22 and -27 inHg. As long as the wafer is dry, vacuum systems experience very few failures in assisting a wafer chuck to hold and retain a wafer. However, during chemical-mechanical polishing, cleaning and other semiconductor processing steps, the wafer may be exposed to deionized (DI) water, slurry or other effluents used during the processing of the wafer.
A common problem for vacuum systems used to hold effluent covered wafers is that effluent may be sucked into the vacuum system and plug the valves or foul the vacuum pump. This problem is especially troublesome since the effluent sometimes enters a vapor stage under vacuum conditions making it difficult to effectively remove the effluent from the vacuum system.
Another common problem is that it is difficult to know when a wafer has accidentally been dislodged from the wafer chuck, known as a "lost wafer condition". If the wafer chuck continues to operate as if the wafer were still firmly held, a valuable wafer might be broken and other wafers and the processing station may also be damaged.
Yet another problem is that effluents can build up in the vacuum system and plug the vacuum lines, valves and vacuum pump. If this "excessive effluent condition" is not detected, it will cause the vacuum system to lose its vacuum thereby making it easier for the wafer to become dislodged from the wafer chuck.
What is needed is a vacuum system in fluid communication with a wafer chuck for reliably holding effluent covered wafers. The vacuum system must be able to remove vapor and liquid effluents that have entered the vacuum system and signal the system computer to take corrective action if a "lost wafer condition" or an "excessive effluent condition" is detected.